Electronic "expression" of the inward rectifier in cardiocytes derived from human-induced pluripotent stem cells

Background Human-induced pluripotent stem cell (h-iPSC)-derived cardiac myocytes are a unique model in which human myocyte function and dysfunction are studied, especially those from patients with genetic disorders. They are also considered a major advance for drug safety testing. However, these cells have considerable unexplored potential limitations when applied to quantitative action potential (AP) analysis. One major factor is spontaneous activity and resulting variability and potentially anomalous behavior of AP parameters. Objective To demonstrate the effect of using an in silico interface on electronically expressed I_K1, a major component lacking in h-iPSC-derived cardiac myocytes. Methods An in silico interface was developed to express synthetic I_K1 in cells under whole-cell voltage clamp. Results Electronic I_K1 expression established a physiological resting potential, eliminated spontaneous activity, reduced spontaneous early and delayed afterdepolarizations, and decreased AP variability. The initiated APs had the classic rapid upstroke and spike and dome morphology consistent with data obtained with freshly isolated human myocytes as well as the readily recognizable repolarization attributes of ventricular and atrial cells. The application of 1 μM of BayK-8644 resulted in anomalous AP shortening in h-iPSC-derived cardiac myocytes. When I_K1 was electronically expressed, BayK-8644 prolonged the AP, which is consistent with the existing results on native cardiac myocytes. Conclusions The electronic expression of I_K1 is a simple and robust method to significantly improve the physiological behavior of the AP and electrical profile of h-iPSC-derived cardiac myocytes. Increased stability enables the use of this preparation for a controlled quantitative analysis of AP parameters, for example, drug responsiveness, genetic disorders, and dynamic behavior restitution profiles.